The present invention relates to laser surgery for correcting myopia and hyperopia and in particular to a shield to protect the peripheral portions of the cornea from the laser during the course of such surgery.
Laser surgery can be used to remove portions of the cornea of the eye thereby reshaping the cornea to correct myopia and hyperopia. During such surgery, a portion of the cornea is removed by the laser thereby reshaping the surface of the cornea to change the focal length of the lens to compensation for the effects of myopia and hyperopia.
To undertake such surgery, it is desirable to remove the upper surface of the cornea such that the lower portion of the cornea is exposed to the laser during surgery. After the laser has reshaped a lower portion of the cornea, the upper surface is replaced and eye is allowed to heal.
A preferred procedure known as Laser Assisted Interastromal Keratomileusis, commonly known as xe2x80x9cLASIKxe2x80x9d, involves the cutting of a dome shaped cap from the cornea with a portion of the cap still attached to the cornea to form a hinge. The cap is then folded backwards to expose a lower portion of a cornea. The laser is then used to reshape the lower portion of the cornea, and after the lower portion has been reshaped the cap is repositioned and allowed to heal. The procedure is described in Dishler U.S. Pat. No. 5,807,380.
During LASIK surgery, the laser beam should be directed at only the lower portion of the cornea exposed after removal of the cap, and it is undesirable for the laser to strike the peripheral edge of the opening formed when the cap has been removed or the fold which constitutes the hinge allowing the cap to be folded backward. It would, therefore, be desirable to provide an improved method and apparatus for protecting the vulnerable portions of the cornea from damage by the laser during laser surgery.
Briefly, the present involves an apparatus and a method of performing laser eye surgery comprising the steps of cutting a cap a material from the outer surface of the cornea of the eye to form a flap having given outer dimensions and a joined edge forming a hinge. The cap is then folded backwards along the joined edge to expose the lower portion of the cornea which is to be re-contoured by the beam of a laser.
In accordance with the invention, an annular shield is provided having a central opening with dimensions which do not exceed the given dimensions of the perimeter of the cap and having a concave lower surface which is complimentary to the shape of the outer surface of an eye. Preferably, a plurality of such shields are provided, with each of such shields having a different sized central opening such that a shield having a central opening sized to best fit the size of the cap of the cornea can be selected for use with the eye undergoing surgery.
The annular shield is positioned with the lower surface thereof upon the eye and over the folded flap with the lower portion of the cornea exposed through the central opening. Thereafter, the laser beam is directed through the central opening to perform the surgery. In accordance with the present invention, the shield""s lower surface is concave and complementary in shape to the outer surface of the eye and the central opening is sized to expose the lower layer of the cornea visible as the result of the removal of a portion which forms the cap. The cap is not entirely removed from the cornea, but is retained thereon by a small portion of the cornea, which serves as a hinge to allow the cap to be folded away and expose the lower portions thereof.
In the preferred embodiment, the central opening comprises approximately 270 degrees of a circle and the remaining 90 degrees is a cord connecting the distal ends of the partial circle. Since the shape of each patient""s eye is different, a plurality of shields, each with a different sized central opening, are provided such that a shield having the central opening suitable for use during the surgery of a given eye is selected. Preferably, each shield is provided with a tab which can be grasped by a pair of tongs or any other suitable device for positioning the shield on the cornea of the eye with the cord of the central opening positioned along the crease of the fold to thereby protect the fold from the rays of the laser.